1. Field of the Invention
This invention relates generally to a flexographic printer, and, in particular, to such a printer which utilizes an improved reverse angle doctor blade assembly.
2. Description of the Prior Art
The function of a conventional doctor blade asssembly in association with a flexographic printer is to remove excess ink from the surface of the anilox roll and provide a uniform ink film to a printing roll over a broad range of ink viscosities and press speeds. However, in recent years, the demand for improved quality in flexographic printing at higher operating speeds has resulted in the development of the reverse angle doctor blade assembly in association with an anilox roll or ink roll, both terms being synonymous in the printing industry. The reverse angle doctor blade assembly shears the ink from the surface of the anilox or ink roll and has the advantage over the conventional doctor blade assembly of removing small particles of dust, pigments, and similar contaminants from the surface of the anilox roll which might otherwise work their way between the blade and the anilox roll and thereby cause undesirable streaking.
By utilizing the reverse angle doctor blade assembly, no surface ink film remains on the anilox roll except for that which is contained in the cells of the cylindrical surface of the anilox roll. As a result, the reverse angle doctor blade assembly virtually eliminates the possibility of streaking by removing contaminants from the cylindrical surface of the anilox roll at the line of contact of the doctor blade with the surface of the roll. In addition, the reverse angle doctor blade assembly requires less critical adjustment of the doctor blade than in the case of conventional doctor blade assemblies.
While the use of the reverse angle doctor blade assembly provides distinct advantages to a flexographic printer, the use of the same has also been found to present certain drawbacks. For example, it is believed that the use of the reverse angle doctor blade assembly may result in increased wear of the anilox roll. In particular, the anilox roll is provided with a cylindrical surface covered with hard chrome plating which, if removed, results in the exposure of a steel base material which wears very quickly and which corrodes when exposed to moisture. Corrosion and excessive wear of the steel base of the anilox roll necessitate the remaking of the surface of the anilox roll. Thus, maintenance of the ink anilox roll is of considerable importance both with respect to the quality of printing obtained, as well as the maintenance costs associated with maintaining the proper condition of the ink or anilox roll.